Keywords: Long COVID, Caloric restriction, Post-COVID-19 condition, Ambulatory intervention, Therapeutic fasting;

Background:

Long COVID (LC), or post-COVID-19 condition, affects approximately 10–20% of individuals following acute SARS-CoV-2 infection, often leading to fatigue, cognitive dysfunction, and reduced quality of life. Effective treatment strategies remain scarce. Fasting and caloric restriction have shown potential benefits in chronic conditions, yet their application in LC, particularly within ambulatory care, remains underexplored. This pilot study aimed to evaluate the feasibility and preliminary effects of a 7-day structured caloric restriction protocol in individuals with LC.

Research questions:

Can a structured, ambulatory 7-day caloric restriction protocol (Buchinger-Wilhelmi method) be feasibly implemented in individuals with LC?
What are the preliminary effects on clinical, psychological, and biological outcomes?

Method:

Twenty individuals with LC were enrolled in a 7-day supervised fasting program (≤350 kcal/day) based on the Buchinger-Wilhelmi method. Assessments were conducted at baseline, daily during the intervention (via phone and online monitoring), post-intervention, and at one- and three-week follow-ups. Biological samples (blood, stool, urine) and validated psychometric instruments (FAS, PHQ-9, GAD-7, WHOQOL, WHODAS 2.0) were collected. The primary endpoint was feasibility, assessed by adherence, safety, tolerability, and data completeness. Secondary exploratory outcomes included changes in clinical, psychological, and biological parameters.

Results:

Nineteen of 20 participants completed the intervention (95% adherence), with only one dropout. At the time of reporting, two participants had reached day 6 of the intervention. The ambulatory caloric restriction model proved logistically feasible, well tolerated, and showed early indications of symptomatic improvement. Biological samples were successfully collected for future analyses, including cytokine profiling, microbiome assessment, immune and dementia biomarkers, mitochondrial dysfunction, and DNA methylation.

Conclusions:

This pilot study supports the feasibility of implementing structured caloric restriction protocols in ambulatory LC care. Such integrative, non-pharmacological interventions may expand the role of primary care and family physicians in managing complex chronic conditions. Larger controlled trials are necessary to evaluate clinical efficacy.

Points for discussion:

Can ambulatory fasting be a potential intervention to improve symptoms in LC patients?

What training or support do clinicians need to deliver such interventions safely and effectively?

Can this ambulatory model inform broader approaches to managing chronic illness in primary healthcare and outpatient settings?